Characteristic feeding method Bathyporeia pelagica is an epistrate feeder, individual sand grains are rotated by the mouth parts and organic matter removed, essentially 'sand-licking' (Fish & Fish, 1996).Pelagic phaseSpecies of the amphipod genus Bathyporeia leave the protection of the sand at night to swim. Such activity is also a feature of certain species of benthic amphipods, particularly of those belonging to the families Haustoriidae, Phoxocephalidae, Oedicerotidae, Calliopiidae, Atylidae and Dexaminidae (Fage, 1933). The swimming activity of Bathyporeia pelagica shows both a circatidal and circasemilunar periodicity (Watkin, 1939a; Fincham, 1970a & 1970b; Preece, 1971). Bathyporeia pelagica emerges on the early ebb of high tides, and is two or three times more active on night-time tides than during the day. It is likely that endogenous rhythm of Bathyporeia pelagica is modulated by temperature, the natural Light/Day cycle (nL/D) and tides acting as exogenous synchronizing factors. This endogenous rhythm will also 'free-run' in animals kept under constant environmental conditions (Fincham, 1970b). However, it is not yet known which exogenous stimulus is most important in re-phasing the activity cycle to keep in tune with seasonally changing tides and nL/D ratios (Hayward, 1994). It is difficult to state exactly why Bathyporeia pelagica has this activity rhythm. Feeding is an unlikely cause since this is conducted whilst buried in the sand. It seems more likely that swimming is connected with the reproductive cycle. Whilst the species swims most nights, a maxima occurs 4-9 days after a new moon when there is less rapid water movement over the beach than at spring tides. As a result mating couplings may be more successful (see reproduction).